1. Field of the Invention
The present invention relates to methods for preparing a titanium-silicalite molecular sieve, and more particular to, a method for preparing large particles of titanium-silicalite molecular sieves.
2. Description of the Prior Art
Crystalline titanium-silicalite molecular sieves are formed by incorporating titanium into the zeolite structure of silicon dioxide, and have the MFI structures, which are also named as the TS-1 molecular sieves. U.S. Pat. No. 4,410,501 discloses the preparation of this molecular sieve. Such a molecular sieve is used as a catalyst in an oxidation reaction with the use of hydrogen peroxide as an oxidant. The particle of this molecular sieve is about 0.2 μm. However, such a catalyst with a diameter of about 0.2 μm applied in the industry (such as the preparation of cyclohexanone oxime from cyclohexanone, ammonia and hydrogen peroxide) still needs to be improved. Thus, the following technologies are developed to enlarge the particle of the molecular sieve, U.S. Pat. Nos. 5,500,199, 6,106,803 and 6,524,984 disclose that small particles are aggregated by an inorganic adhesive agent, and then spry-dried. The particle of the catalyst in these methods is enlarged; however, the active site of the catalyst is covered by the adhesive agent, the reactivity of the catalyst is decreased, and the amount of the catalyst in the reaction needs to be increased.
Hence, it is an urgent issue to develop a method for preparing a titanium-silicalite molecular sieve with a large particle size and high activity so as to facilitate the recovery of the molecular sieve, improve the usage efficiency of hydrogen peroxide, and favor the application in the industry.